期刊
CARBOHYDRATE RESEARCH
卷 329, 期 4, 页码 839-845出版社
ELSEVIER SCI LTD
DOI: 10.1016/S0008-6215(00)00227-5
关键词
dielectric relaxation; glass transition; water; mixtures
The dielectric relaxation behaviour of several amorphous low molecular weight carbohydrates and their 10% w/w water mixtures has been studied in the supercooled liquid and glassy regions in the frequency range 100 Hz to 100 kHz. The dry carbohydrates show a primary alpha -relaxation (activation energy 250-405 kJ mol(-1)) at temperatures above the calorimetric glass transition temperature, T-g, and, in most cases, a secondary p-relaxation (activation energy 42-55 kJ mol(-1)) at sub-T-g temperatures. Whilst D-mannose showed a beta -relaxation similar in strength to D-glucose, its deoxy sugar, L-rhamnose showed a relatively weak beta -relaxation. This indicates that the hydroxymethyl group influences relaxation in carbohydrate glasses. Addition of water shifted the alpha -relaxations to lower temperatures and increased the strength of the beta -relaxations. In glucitol this resulted in a merging of the alpha- and beta -relaxations. The beta -relaxation increased in strength and decreased in temperature for the series of water mixtures: D-glucose, maltose, and maltotriose. (C) 2000 Elsevier Science Ltd. All rights reserved.
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